What are you hoping to achieve by using a separate mic input?
If you are concerned about low light, I take it you expect to be recording these concerts from some distance away (like, in the audience). If you use a separate mic to just plugin , and still use near the camera location, then I'm afraid you'll probably be a bit disappointed with the results. The problem with recording indoor sound from any distance is that you also record all the room echo as well, and it still tends to sound, well, rubbish!
To make any real difference in sound quality you have to get near to the sound source with your microphone.
Favourite ways to do that are either with radio mics, where you take the mic and it's transmitter near to the source to be recorded, and plug the receiver into your camera mic input, or another (cheaper) option is to use a separate audio recorder (solid state, minidisc,etc) and mix the sound tracks in your video editing software afterwards.
For the second option, you don't need a mic input on your camera .
Unless of course,I've missed the point and you are intending to do something completely different !